Pure fluid force generator



R. E. BOWLES PURE FLUID FORCE GENERATOR Sept. 16, 1969 Filed Nov. 18. 1966 4 Sheets-Sheet l CONTROL FLUI D SOURCE FIGJ.

i-CHORD PIC-3.3

IO J I INVENTOR ROMALD E. BOWLES CHORD Szmmkw m0 wmDmmwma 2.52%

ATTORNEYS Sept. 16, 1969 R. E. BOWLES 7,

. PURE FLUID FORCE GENERATOR Filed Nov. 18, 1966 4 Sheqts-Sheet 2 WATER SURFACE v INVENTOR ROMALD E. BOWLES PURE FLUID UPPER SURFACE E FORCE BY ldl/ I GEN. STARBOARD 335 $8355 GEN LOWER SURFACE ATTORNEYS Sept. 6, 1969 R. a. sown-:5

PURE mun FORGE esuamon 4 Sheets-Sheet 5 Filed Nov. 18, 1966 DOWN CONTROL LINE SIDE CONTROL LINE- -SIDE CONTROL LINE EXTERNAL SHEATH DOWN FORCE EXTERNAL SHEATH SIDE FORCE u CONTROL LINE INVENTOR ROMALD E. BOWLES ATTORNEY S Sept. 16, 1969 R. E. BOWLES PURE FLUID FORCE GENERATOR 4 Sheets-Sheet 4 Filed Nov. 18, 1966 INVENTOR ROMALD E. BOWLES ATTORNEYS United States Patent 3,467,043 PURE FLUID FORCE GENERATOR Romald E. Bowles, Silver Spring, Md., assignor to Bowles Engineering Corporation, Silver Spring, Md., a corporation of Maryland Filed Nov. 18, 1966, Ser. No. 595,530 Int. Cl. 1863]) 1/26; B63h 5/14 U.S. Cl. 114-665 27 Claims ABSTRACT OF THE DISCLOSURE A pure fluid force generator comprises foil structure having a depression formed in at least one of its surfaces to which pressurized control fluid is provided at an adjustable flow rate. The depression is formed along a portion of the foil chord length corresponding to a foil surface region of low pressure when the foil is immersed in a fluid stream. The flow rate of the control fluid into the depression can be adjusted to provide a greater pressure in the depression than the pressure produced by the fluid stream, whereby a resultant force is applied to the foil in the depression.

The present invention relates to pure fluid force generators and, more particularly, to systems for affecting the course and movement of craft which are normally propelled through relatively frictionless media such as water, air, or other fluid-filled space.

Systems for controlling the motion of craft which move through fluid media have conventionally been of the moving foil, moving rudder or reaction jet types. For many applications, these systems are quite satisfactory but have inherent disadvantages such as complexity, sluggish response, and relatively high cost of procurement and maintenance which render them unsuitable for other applications. These and other disadvantages are overcome by means of the pure fluid force generator of this invention.

Briefly, this invention makes use of the surface pressure distribution created at the surface of an airfoil or hydrofoil as a function of the velocity of a fluid stream in which said foil is situated. As is well known in aerodynamic and hydrodynamic theory, when a foil is in a fluid stream, portions of its surface are subjected to lower pressures than others; some of these portions experiencing pressure which are negative with respect to the static pressure of the overall fluid stream when the local fluid stream exceeds a certain predetermined stream velocity. This fact accounts in part for the lift forces essential to operation of airplanes and hydrofoil vehicles.

It has been found that, when fluid is introduced into a low pressure region adjacent a foil surface and the fluid introduced has a pressure exceeding that at said low pressure region of foil, a force is exerted on the foil surface, said force being directed against the adjacent foil surface and normal thereto. Applying this teaching to a zero camber foil, which is symmetrical about its root chord line, it is possible to control the normal force, sense and amplitude, and so steer the foil to one side or another of the chord axis as it moves through a fluid medium by merely applying appropriate flow rates of control fluid to one or the other of the foil surfaces.

Prior art attempts to take advantage of this theory have proved unfeasible because the control fluid, when applied along the natural foil surface, interacted in an unpredictable manner with the main fluid stream lines so as to produce turbulence, discontinuities of control with respect to control fluid flow changes, instability at particular flow rates of the control fluid, and hysteresis effects. It has been found that, by providing a step-shaped depression in the foil parallel to the leading edge and located approximately at the point of maximum foil thickness and by Patented Sept. 16, 1969 supplying the control fluid so that it flows from within this surface depression, a pressure bubble is created within the natural stream lines. The resulting apparatus is free of many of the disadvantages of the prior art devices and is capable of a smooth and rapid response, has substantially no moving parts, and requires minimal maintenance.

The pure fluid force generator outlined above may serve as a steering control for water craft by rigidly securing the foil to the craft so that it extends vertically therefrom and parallel to the longitudinal axis of the craft. If the foil is symmetrical about its chord line, the pressure distribution along the surfaces of the foil caused by motion of the craft through the water parallel to the chord is equal at corresponding chord locations on both surfaces of the foil. The net turning force acting on the foil is therefore Zero when no control fluid is supplied. If a flow of gas is supplied to the depression on one of the surfaces through appropriately situated bleed vents, a pressure bubble is developed between the stream and that portion of the foil surface rearward of the leading surface of the step. The static pressure in the bubble is greater than the static pressure at the corresponding surface location on the other side of the foil and a net force is directed toward the foil which tends to move the foil in a direction away from the bubble. Since the foil is rigidly secured to the craft so as not to rotate with respect thereto, the force turns the craft to the degree and in the direction determined by the control fluid flow rate.

The effectiveness of the aforesaid device reside primarily in the ability to maintain a well-defined bubble in which a uniform pressure may be maintained and the pressure varied as a function of the rate of flow of gas into the bubble. Positive definition of the bubble is achieved because of the fact that the rate of entrainment of air in water at the interface between the bubble and the water is low relative to the rate at which air or other suitable gas can easily be supplied. Thus, a controllable pressure may be developed on one side or the other of the foil in a specified region defined by the bubble. The operation of such a device does not depend on a boundary layer spoiling effect as in prior art jet control of foils and, in consequence, does not suffer flow separation and the resulting turbulence and energy losses incident thereto.

The above description of operation applies in every respect to a gas-in-gas control except that entrainment at the gas-gas interface is more effective than in the gasliquid system. The practical result is that it is diflicult to maintain a uniform pressure in the bubble and the system is less effective than in the gas-liquid case. However, the system still performs better than the spoiler type systems since pressure control is obtainable in a specified region and operates over a determinable area of the foil.

As described in detail below, additional applications of the principles of this invention reside in stabilization controls, three-dimensional translation and rotation control, thrust generation, and the like.

Accordingly, it is an object of this invention to provide a pure fluid force generator of simple construction, having a rapid and smooth response to applied control conditions, and requiring minimal maintenance.

It is another object of this invention to provide a pure fluid force generator which has practical application in controlling the motion of air, water and craft operating in other fluid environments.

It is still a further object of this invention to provide a novel foil structure to control the motion of craft designed to move through a fluid.

It is another object of this invention to provide a modified airfoil or hydrofoil structure in which a portion of the surface has been removed for the purpose of accommodating a control fluid flow at that surface, the control 3 flow being effective to change the pressure distribution acting on the foil.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a side view of the pure fluid force generator of this invention, illustrating entrance and flow of the control fluid;

FIGURE 2 is a cross-sectional view through lines 22 of FIGURE 1;

FIGURE 3 is a plot of surface pressure distribution versus chord line of a foil exposed to a fluid stream, said plot being useful in describing the operation of the pure fluid force generator;

FIGURE 4 is a perspective view of the embodiment illustrated in FIGURES l and 2 as applied to a steering control for a small boat;

FIGURE 5 is a perspective view of the pure fluid force generator employed as a steering control in a hydrofoil craft;

FIGURES 6 and 7 are side and rear views respectively of an ocean vessel employing the pure fluid force generator of this invention as a roll stabilization device;

FIGURE 8 is a view in perspective of the pure fluid force generator of this invention employed as a shroud for a pump jet;

FIGURE 9 is a cross-sectional view taken along line 99 of FIGURE 8;

FIGURE 10 is a schematic diagram illustrating the operation of a plurality of embodiments depicted in FIG- URE 6;

FIGURE 11 is a perspective view of still another embodiment of this invention.

Referring now specifically to FIGURES 1 and 2 of the drawing, one embodiment of the pure fluid force generator of this invention is represented generally by the reference numeral 1. It is seen that this embodiment takes the form of a substantially planar foil, symmetrical about its chord line (zero camber). On each surface of the foil, there is a substantially step-shaped depression 5 which extends across the span of the foil between predetermined points on the chord line of the foil. As is explained in detail below, if the ratio of the span of the foil to the foil length is large, the step 5 may extend across the entire foil. If the ratio is small, certain modifications must be made as discussed relative to FIGURE 4.

The step 5 is formed in the foil at or closely adjacent to the maximum thickness of the foil. This is necessary so that the configuration of the stream lines about the foil are substantially unchanged by the step. This latter consideration is controlling and permits a small variation of the location of the step relative to the point of maximum thickness of the foil.

While the depressions 5 in the foil surfaces may take any one of a number of shapes, the step shape employed herein has been found to give the best results with respect to overcoming the disadvantages present when no depression is utilized. As best illustrated in FIGURE 2, the step depression 5 is bounded by two sides, each of which extends along the entire foil span. One side 51 lies in a plane perpendicular to the plane of the chord; and the other side 52 is generally parallel to the chord.

Extending interiorly of and across the span of the foil, adjacent the intersection of walls 51 and 52 are two manifolds 2. These manifolds are employed to convey control fluid from a controlled fluid source 7 to a series of vent fluid outlets 4 extending into the depression at the intersection of the walls 51 and 52 at spaced intervals across the entire width of the foil. Controlled source 7 supplies control fluid to the two vent manifolds via fluids paths 71 and 72. Control valves 73 and 74 in paths 71 and 72 provide a means to adjust the control flow rate to achieve the desired turning force on the appropriate side of the foil. This control means, as illustrated, is only intended to be representative of a means to provide plural independently adjustable fluid control flow rates, and any appropriate means for accomplishing this function, such as pure fluid amplifiers, may be employed. For instance, the source 7 may be atmospheric air where the depressions 5 are operating below atmospheric pressure.

If the foil illustrated in FIGURES 1 and 2 is placed in a fluid stream at a zero angle of attack (i.e., the leading edge 8 facing the on-coming fluid stream and the chord line parallel to the stream) a surface pressure distribution curve such as illustrated in FIGURE 3 is created on each surface. The vertical axis in FIGURE 3 represents the surface pressure coefficient, which is a measure of the surface pressure on the foil with respect to static pressure of the stream, while the horizontal axis represents distance along the chord line. It is seen that, over a section of the chord length, the surface pressure coefficient is negative (i.e., the surface pressure is less than the static pressure of the fluid stream). As the velocity of the fluid stream increases, the absolute pressure at the foil surface represented by the negative portion of the curve becomes less.

The curve of FIGURE 3 represents the basic nature of conditions over an extended range of operating speeds. Amplitudes vary with speed but the overall curve slope does not change until speeds are sufliciently high to produce separation of the flow from the foil surface. This latter region of operation is of no concern in the present application and is not discussed further.

The curve of FIGURE 3 represents the pressure distribution of both foil surfaces for a symmetrical foil at zero angle of attack. Actual operation of the foil of the present invention depends upon the fluid medium in which the foil operates and the control fluid. Thus, three practical cases present themselves: gas control flow in a liquid environment, liquid control flow in a liquid environment and gas control flow in a gas environment.

In the first type of operation, gas in liquid, the region between the liquid flowing over the foil and the wall 52 should be maintained at above the vapor pressure of the liquid so that cavitation does not occur. If cavitation were permitted to occur, shock waves produced by collapse of cavitation bubbles would produce erosion on the foil as well as introducing unnecessary turbulence into the system.

As indicated above, cavitation can be prevented, in those instances where normal operation of the foil would produce pressures in the depression 5 below the vapor pressure of the liquid, by supplying continuously suflicient gas to the depression 5 to maintain the pressure above the vapor pressure of the liquid. The flow required is a function of many factors such as foil design, speed, depth of foil in the liquid, etc.

The operation of the foil depends upon supplying fluid to one or the other of the cavities so as to increase the pressure in one of the depressions 5 relative to the other depression. In the system under discussion, entrainment of the gas at the gas-liquid interface is relatively ineflicient so that a distinctive gas bubble is formed. In the ideal case, no gas would be entrained by the liquid and, as gas is fed to the bubble, the pressure therein would increase without loss except at the downstream end of the depression 5. In this case, the pressure in the bubble is a function of net flow of fluid, i.e., the difference between the rate of flow of gas into the bubble through vents 4 and flow out of the bubble toward the trailing edge of the foil. Entrainment of gas, although small relative to a liquid-liquid or gas-liquid system, is still a factor in operation of the system. Thus, ideal operation cannot be obtained but a quite uniform pressure can be maintained in the systems and at practical flow rates.

In a gas-gas or liquid-liquid system, momentum effects must be considered as well as increased entrainment. In the gas-liquid system, the momentum (mass X velocity) of the gas is small relative to the momentum of the liquid. In the other two types of systems, however, the density of the fluid is the same as or close to the density of the ambient fluid and momentum effects become significant. Thus, if a gas control stream is issued at some angle relative to wall 52 into depression 5, this stream contacts the adjacent stream of ambient fluid and a substantial portion of its dynamic pressure /2pV is converted to static pressure. Thus, in these types of systems, there is obtained a two-fold pressure effect, pressurization of the bubble due to a net flow of fluid into the depression 5 and momentum derived pressures.

This added feature in the gas-gas and liquid-liquid systems is at least partially offset by the increased entrainment in these systems due to similarity of fluids.

In the gas-liquid system, it is considered desirable to feed a gas to the bubble to prevent cavitation. It is considered desirable to feed control fluid in all of the various types of systems in suflicient quantity to cause the ambient fluid to follow the same flow path, in the absence of a control signal, that the fluid would follow if the depressions 5 were not present. Such operation insures maximum operating efliciency of the foil under normal conditions.

An additional advantage to the use of control flows to the step at all times is that the drag is reduced considerably, the minimum drag being achieved when maximum control flow is present. However, if equal amounts of control fluid are normally supplied at some restricted flow rate, a greater turning capability is provided, since a simultaneous increase in flow on one foil surface and decreases on the other is made possible. This push-pull type of operation is desirable in many applications and thus an optimum condition can be reached by balancing turning power requirements, permissible drag and minimum consumption rates of control fluid.

The above establishes minimum flow for the system if maximum foil effect is required. Maximum flow is determined by the situation where the control fluid flow around the trailing edge of the foil to the other surface. Thus, control fluid may be introduced until the bubble extends back to the trailing edge of the foil and perhaps a little further depending upon velocity of flow. However, a point is reached where control flow starts up the other side of the foil and this must be avoided. It should be noted that by causing the bubble to extend to the trailing edge of the foil, a pressure increase is effected along the entire surface downstream of wall 51 and maximum force is developed on the foil. Thus, by varying flow between that required to maintain normal stream lines about the foil and formation of a bubble extending to the trailing edge, a continuous range of forces between two extremes may be obtained to impart turning moments to a body to which the foil is attached. By employing foils at opposedlocations on a body, such as the two wings of a plane, and by developing forces on the same side of the foils (for instance, underside of the wings) translatory movement can be achieved.

The preferred size of the step with respect to the chord line is determined from the surface pressure distribution curve of FIGURE 3 for the particular foil structure, and from system requirements (i.e., range and type of forces required, expected ambient conditions, etc.). In a typical embodiment, surface 52 may extend across the entire foil span and between the .3 and .6 chord points, this latter factor being determined by the depth of the depression 5. As seen in FIGURE 3, the .3 and .6 chord points are within the negative surface pressure regions for most foil structures.

It is necessary to proper operation of the foil that the control fluid, which is at a higher pressure than much of both foil surfaces, be prevented from flowing around the ends of the foil and increase the pressure on both surfaces rather than the one surface intended. One solution to this problem is to apply the control fluid flow over a smaller portion of the foil surface. This type of operation can be accomplished by omission of the step 5 at regions close to the ends of the foil. Alternatively, the effect will be small if the aspect ratio of the foil is large, at least 3 to l, and preferably higher, so that the quantity of control fluid effected by end flow is small relative to the total quantity of control fluid employed. It has also been found that, by securing end plates 9 on either end of the foil, as illustrated in FIGURE 4, the control fluid does not travel from one foil surface to the other even when the entire surface area of the step is subjected to large flow rates of control fluid. These end plates 9 have been found to be most effective when positioned such that the longitudinal axis of each plate lies in the plane of the chord of the foil. Preferably, the length of the plates should be slightly greater than the length of the foil, while the width of the plates should be approximately twice the width of the foil.

FIGURE 4 also illustrates a basic application of the pure fluid force generator of this invention, namely, a steering control for water surface craft. Craft 11 is illustrated as having rigid support member 10 extending vertically from its stern below the surface of the water. Member 10 has depending therefrom the pure fluid force generator ll, said generator being rigidly secured to member 10 at upper end plate 9 such that the generator is incapable of motion along any axis with respect to craft 11. The pure fluid force generator is thus entirely below the water surface and causes the craft 11 to rotate in accordance with application of a differential force to the two foil surfaces. Member 10 may preferably include means to transport control fluid (such as fluid paths 71 and 72 of FIGURE 1) to the vent manifolds 2 of FIGURE 1. For this application, the control fluid may well be air at atmospheric pressure, since for shallow depths the free stream static pressure in the region of the steps 5 is lower than atmospheric pressure for most practical velocities. A limitation exists here, however, in that at very low velocities of the fluid stream with respect to the foil, the surface pressure on the foil is not sufliciently negative with respect to the static pressure of the stream so as to be lower than the atmospheric pressure. Thus, While a given flow rate produces increasing turning force with increasing velocity, no steering control would exist at very low velocities, regardless of the magnitude of the flow rate, unless a control fluid at somewhat greater pressure were employed. In addition, where the foil is submerged to a depth at which the free stream static pressure is such that the static pressure in the step exceeds atmospheric pressure, a control fluid at greater pressure is required. Whether or not the higher pressure is necessary depends on the particular application; but whatever control fluid is chosen, it is readily apparent that the pure fluid force generator 1 provides a relatively simple means for steering the craft 11 without requiring any moving parts other than those necessary to regulate the rate of control fluid flow.

An interesting characteristic of the foil when employed as a steering control substantially as described above is the fact that the turning force created by a given control flow rate changes in accordance with the angle of attack of the chord line of the foil with respect to the velocity vector of the free fluid stream. As is well known in the fields of aerodynamics and hydrodynamics, as the angle of attack of the foil changes the pressure on the foil surface facing upstream increases while the pressure on the surface facing downstream decreases. Applying this to the embodiment of FIGURE 4, assume that craft 11 is moving through the water at some velocity so as to create equal and determinable surface pressure distributions on both foil surfaces. Applying a control fluid flow to the step 5 on the starboard surface of the foil produces a greater pressure on that surface, with the result that the craft turns in the starboard direction. As the craft turns, the port surface of the foil faces upstream of the water stream thereby creating an increased pressure on the port surface. The magnitude of this increased pressure resulting from change in angle of attack depends on the turning rate of the craft and in turn on the flow rate of the control fluid, there being a larger instantaneous upstream exposure of the port surface for greater starboard turning rates. Thus, the pure fluid force generator tends to rate limit itself as a function of the input control signal, essentially providing a stabilizing negative feedback. Specifically, a turning force is countered by a change in pressure distribution which is a function of the turn achieved.

A further consideration in the embodiment of FIGURE 4 concerns the requirement that the step depressions in the foil surfaces must be kept isolated from access to atmosphere except through the vent manifold 2 and associated outlets 4. Clearly such access would cause a loss of control of the control fluid bubble created by the control fluid flow between the free stream and the foil surface, which bubble in effect supplies the turning pressure required. The top end plate 9 helps in this regard, however, care should be taken that the top plate does not rise above the surface of the water.

The configuration illustrated in FIGURE 4 was tested using a standard NACA 63 -018 foil, modified with the step depression discussed above, and secured to a water craft. The foil, when fluid flow was applied as discussed above, provided a smooth and quick-responding steering control.

Prior to this invention, the conventional rudder had been the most reliable and rugged steering device. It should be apparent that this novel pure fluid force generator is inherently more rugged, more reliable, less expensive, and faster acting, and needs less maintenance than even the simplest available rudder mechanism. Whereas, in a small boat steering mechanism and in smaller hydrofoils, atmospheric air may be employed, the control power requirements are smaller than in conventional systems. This latter statement is true in many other applications where the foil is not at a considerable depth in water or other dense fluid.

FIGURE 5 illustrates another application of the pure fluid force generator; namely, a steering control for a hydrofoil craft. Strut 13 is rigidly secured to and dependent from a craft (not shown) which is moving above the surface of the water. Below the surface pod 15 is secured to strut 13 with hydrofoil sections 12 and 14 extending horizontally in opposite direction from the pod, The pure fluid force generator 1 is rigidly secured to the pod 15 and vertically dependent therefrom. Lower end plate 9 is illustrated as secured to the bottom end of the pure fluid force generator while pod 15 and hyddrofoils 12 and 14, in addition to their conventional functions, serve as a top end plate for the generator. The embodiment of FIGURE 3 operates in a manner similar to that of FIGURE 4. It should be noted that hydrofoil craft are capable of operating at greater speeds than are conventional water craft and therefore will generally not require as high a pressure for the control fluid as will the water craft at respective normal operating speeds. In addition, the hydrofoil may operate sufliciently close to the surface to permit the use of atmospheric air as the control fluid as discussed above for the embodiment of FIGURE 4.

It is apparent that the foils 12 and 14 or one of them may also be stepped foils. In, for instance, a hydrofoil having two forward pods each with stepped foils for the planes, roll stabilization may be effected by application of control flow differentially to the upper and lower surfaces of the foils of the two pods. Depth control is effected by supply of control flow to corresponding surfaces of the foils of the two planes. Steering may be effected by employing a vertical foil 1 below each plane and applying control flow differentially to these foils. Other types of control are obvious by extension of the stepped foil to the rear pod of the hydrofoil to provide roll about the three rotational axes and translation in two planes.

A still further application of the pure fluid force generator of this invention is as a roll stabilization control for other water craft as illustrated in FIGURES 6 and 7. The conventional method of providing roll stabilization for large water craft is to appropriately position large foilshaped fins at the sides of the craft and then change the angle of attack of the fins upon a command from a computer control, the latter receiving information from various attitude sensors. This method can advantageously be improved upon by employing a series of stationary pure fluid force generators in place of the rotating fins, the generators responding to similar computer commands. Such a craft 14 is illustrated in FIGURES 6 and 7. A plurality of pure fluid force generators 1 are secured to both the port and starboard sides of the craft, normally disposed so as to have zero angle of attack with respect to the free fluid stream created by movement of the craft through the water. In addition, the generators 1 are positioned at some pre-determined angle with respect to the surface of the water. Should the craft exhibit a tendency to roll clockwise as viewed from FIGURE 7, application of an appropriate increase of control fluid flow (as determined by the computer) to the lower surface of the starboard generators and the upper surface of the port generators will provide the necessary counter clockwise corrective movement, Similar decrease in flow at the upper starboard surface and lower port surface may be applied simultaneously to provide an increased control force for minimal flow change. An analogous operation is possible to correct for counterclockwise roll. It should be noted that the depth at which the pure fluid force generators are located in this embodiment is such that atmospheric pressure is ineffective for most practical velocities, and thus a pressurized control fluid is required. As is the case for the embodiment of FIGURE 4, optimum balance between drag considerations and stabilizing force may dictate the maintenance of a restricted control flow at the steps of the foils during stable operation.

Another embodiment of this invention is the modified pump jet shroud 16 illustrated in FIGURE 8. The pump jet shroud is similar to the foil of the previously described embodiments but it is distorted from a planar to a hollow cylindrical shape, thus providing an outer step or depression 40 and an inner step or depression 45.

It is desired to employ the device to produce translation in two planes, up-down and side-to-side or any combination thereof. Thus, it is necessary to separate each surface, inner and outer, of the shroud 16 into four quadrants. On the exterior surface of the shroud, there are provided four ribs or vanes 41 spaced apart and following the normal foil contour from leading to trailing edges. Thus, the ribs 41 perform much the same function as the plates 9 of prior figures. It is apparent that these ribs can be raised above the usual foil surface if necessary for isolating one section of the step 40 from the adjacent sections.

As to the interior surface of the shroud 16, the shroud is intended to be employed with an impeller 46 for purposes to be described subsequently, the impeller constituting the one or one of the screws employed for craft propulsion. The shaft of the impeller may desirably be journaled interiorly of the shroud 16 in a central hub 43 of a spider arrangement. The spider consists of four struts 44 in axial alignment with the ribs 41 so as to divide the step 45 into four quadrants. The struts 44 may be streamlined so as to reduce drag and turbulence.

The shroud cross-section as seen in FIGURE 9 is a cambered foil but basically the design is controlled by velocity considerations, i.e., the system operates at or near maximum efficiency with a constant velocity from front to back interiorly of the shroud, i.e., the interior of the shroud has a constant volume downstream of the impeller. Thus, the exterior contour must take into account the initially increasing and subsequently decreasing cross-section of the struts 44 of the spider, the effect of the hub of the spider which is also streamlined and the subsequent termination of the struts and hub. Specifically, the interior surface of the cross-section of the shroud is parallel to its axis. The exterior surface of the shroud is simply streamlined.

Control fluid is supplied through four lines in a shroud support member 17 and is distributed through manifolds in the shroud or through the struts 44 and the hub.

It is readily apparent that control fluid flow supplied -via appropriate lines 47 to selected portions of the exterior shroud surface can be utilized to produce both side and vertical forces as the shroud passes through the fluid medium. The forces are generated in the same manner as for the planar foil, with the control fluid being applied at depression 18. Dividers 41 divide the shroud surface into four quadrants so that the control fluid flow applied to any quadrant will provide a force against the shroud in the desired horizontal or vertical direction. Further, due to the nature of the pump jet, the fluid flowing inside the cylinder is moving at a greater velocity than that flowing outside, thereby enabling development of even greater side or vertical forces by appropriately applying control fluid along selected portions of the internal surface of the shroud. Further, at low velocities of a craft to which the unit is attached, i.e., at velocities that are sufliciently low that control forces cannot be effectively generated on the outer surface of the shroud, the fluid flowing through the interior of the shroud is at sufficient flow rates due to pump action, to permit control forces to be developed on the interior surfaces of the shroud.

There is illustrated in FIGURE the use of two pump jet shrouds to provide three-dimensional motion control. The letters A through H and I through S associated with pump jet shrouds 16 and 16 respectively, represent different control fluid outlets along selected portions of step depressions on the internal and external surfaces of the shrouds. The shrouds 16 and 16 are shown rigidly supported below the hull of a fluid medium craft 19, such as a ship, symmetrically disposed with respect to the 1ongitudinal axis of the craft. As the craft 19 is propelled through the fluid medium, it is evident that the presence of control fluid flow at the outlets indicated in the table below will produce the indicated force on the craft:

A+D+J+M Down force. B+C+K+L Up force. G+F+R+P Force to right. E-|-H+N-|-S Force to left. A+D+K+L counterclockwise force. B+C+J+M Clockwise force.

Thus, a three-dimensional course control is made possible by this invention, such control having no moving parts except for the means used for regulating the control fluid flow rate.

In FIGURE 11, a further modification of the pure fluid force generator is illustrated. This embodiment comprises a foil structure formed from the locus of the points created by rotating the two dimensional cross-section of foil 1 of FIGURE 2 about its chord line The resultant foil structure 21 has a step depression 22 extending entirely about its perimeter between predetermined chord points and has a plurality of groups of control fluid outlets 23, 24, etc. The cross-section of foil structure 21 is circular at any point along its longitudinal axis. The foil 21 is rigidly secured to an appropriate fluid medium craft 19 by support members 20. Dividers 47 separate the control outlets into four groups 23, 24, etc. As the craft 19 moves through a fluid medium, the surface pressure distribution created uniformly about the foil 21 can be controllably altered by insertion of greater or lesser amounts of control fluid flow at the various control fluid outlet groups 23, 24, etc. The foil structure 21 is thus clearly adaptable to provide both vertical and side forces in a manner similar to that employed for the pump jet shroud of FIG- URE 8, and additionally to provide rotational forces when combined with similar foils on a single craft in a similar manner as indicated for the pump jet shrouds in FIGURE 9. This ultra-simple pure fluid force generator is thus capable of providing three-dimensional course control for various fluid medium craft, the entire control system being easily maintained, inexpensive, and consuming relatively small amounts of power.

Numerous other applications for the pure fluid force generator of this invention will become apparent to those skilled in the art from the above disclosure, thus the scope of the invention should not be limited to the applications discussed herein. For example, certain applications may best be served by asymmetrical foil configurations. Asymmetry of a foil about its chord line produces unequal pressure distributions along the two foil surfaces in a planar type foil (as in FIGURES 1 and 2) and unbalanced pressure distribution along the surface of the three-dimensioned foils (of FIGURES 8 and 11). These unequal and unbalanced pressure conditions produce a bias force against the foil in one direction which may be used to produce a steady control under quiescent conditions (no control signal) or may be balanced out by bias control signals as desired. Similarly, depressions other than those in the form of a step may prove desirable to achieve a particular result. Further, the embodiment illustrated in FIGURES 6 and 7 readily suggests the utilization of the pure fluid force generator of this invention to control yaw and pitch, in addition to roll, by merely relocating the foils to appropriate positions and orientations at the bow and stern of the craft. These and other applications are rightly to be considered within the scope of this invention.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variation of the details of construction which .are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

I claim:

1. A pure fluid force generator, comprising:

a streamlined foil structure having at least one surface and having a first depression in said one surface;

means for providing a determinable surface pressure distribution along the chord of said foil structure at said one surface in response to immersion of said foil structure in a fluid stream;

control means for selectively applying a force to said foil structure at said depression, said control means comprising means for providing control fluid at an adjustable flow rate within a predetermined range of flow rates to said depression, the control fluid flow rate being sufliciently great over a significant portion of said predetermined range of flow rates to provide a pressure on said foil in said depression which is greater than the surface pressure created at said depression on the foil by said means for providing a determinable surface pressure distribution;

wherein said-foil structure is substantially planar and symmetrical about the plane of its chord line, wherein the surface opposite said one surface has a second depression therein which corresponds identically to said first depression in shape and position, wherein said means for providing a determinable surface pressure distribution creates a surface pressure distribution on said opposite surface which at zero angle of attack of said foil structure relative to a fluid stream in which it is immersed is substantially identical to said determinable surface pressure distribution, and wherein said control means includes means for providing an additional adjustable flow rate of said control fluid at said second depression.

2. The pure fluid force generator of claim 1 wherein said first and second depressions are in the shape of a right-angle step in the respective surfaces of said foil, and wherein said control means distributes the control fluid along the base of each said step.

3. The pure fluid force generator of claim 2 wherein said steps extend across the span of the foil between predetermined chord points, and wherein said control means includes a plurality of orifices distributed along the width of each of said steps for admitting said control fluid to said step.

4. The pure fluid force generator of claim 3 further comprising end plate means disposed substantially in perpendicular relation to said surfaces and secured to opposite ends of the foil for preventing leakage of control fluid flow from the foil surface to which said flow is sup plied to the other foil surface.

5. The pure fluid force generator of claim 4 wherein said control means includes vent manifolds associated with each of said steps, said vent manifolds being located beneath the surfaces of said foil, and means for conducting said control fluid between the vent manifolds and the orifices of said respective steps.

6. The pure fluid force generator of claim 5 wherein said control fluid is at a substantially constant pressure.

7. A pure fluid force generator, comprising: a streamlined foil structure having at least one surface and having a first depression in said one surface;

means for providing a determinable surface pressure distribution along the chord of said foil structure at said one surface in response to immersion of said foil structure in a fluid stream; control means for selectively applying a force to said foil structure at said depression, said control means comprising means for providing control fluid at an adjustable flow rate within a predetermined range of flow rates to said depression, the control fluid flow rate being sufficiently great over .a significant portion of said predetermined range of flow rates to provide a pressure on said foil in said depression which is greater than the surface pressure created at said depression on the foil by said means for providing a determinable surface pressure distribution; wherein said foil structure comprises a hollow cylinder having an inner and outer contoured surface, said outer surface corresponding to said at least one surface; wherein each of said inner .and outer surfaces have depressions therein at predetermined regions thereof; wherein said control means provides a pinrality of additional adjustable flow rates of control fluid to said depressions, and wherein said fluid stream in which said foil structure is immersed produces a fluid stream around the outside surface of said cylinder and a second fluid stream of higher velocity through the inner portion of the cylinder, thereby creating different predetermined surface pressure distributions along the inner and outer surfaces of the cylinder. 8. A pure fluid force generator, comprising: a streamlined foil structure having at least one surface and having a first depression in said One surface;

means for providing a determinable pressure distribution along the chord of said foil structure at said one surface in response to immersion of said foil structure in a fluid stream; control means for selectively applying a force to said foil structure at said depression, said control means comprising means for providing control fluid at an adjustable flow rate within a predetermined range of flow rates to said depression, the control fluid flow rate being sutnciently great over a significant portion of said predetermined range of flow rates to provide a pressure on said foil in said depression which is greater than the surface pressure created at said depression on the foil by said means for providing a determinable surface pressure distribution;

wherein said foil structure is a closed three-dimensional body of circular cross-section at any point along its longitudinal axis, and wherein said depression is in the shape of a step which extends about the circum ference of the body between predetermined chord points.

9. In a craft of the type which is propelled through a fluid medium, a control system for changing the orientation, position or course of the craft in its fluid medium, comprising:

a foil structure having at least one surface and a first depression in said one surface said depression having a forward wall located at approximately the maximum thickness of said foil and extending over a large region of the surface of said foil in the plane of said surface;

means for rigidly securing said foil structure to said craft;

means for creating a determinable surface pressure distribution along the chord dimension of said surface in response to motion of said craft in said fluid medium;

control means providing control fluid at an adjustable flow rate to said depression for producing a static pressure on said foil in the region of said depression which is greater than the pressure produced in said region by said means for creating a determinable surface pressure distribution.

10. The combination according to claim 9 wherein said control means further comprises means for flowing said control fluid at a selectively adjustable flow rate along the base of said depression from said leading edge rearwardly of said foil structure such that said control fluid forms a pressure bubble between the natural streamline of said determinable fluid streamline pattern and the base of said depression, the pressure in said bubble varying with the flow rate of said control fluid to selectively vary the pressure applied at the base of said depression.

11. The system of claim 10 wherein said foil structure is substantially planar and symmetrical about its chord; wherein the surface opposite said one surface has a second depression therein which corresponds identically to said first depression in shape and position; wherein said fluid stream producing means creates a surface pressure distribution on said opposite surface which is substantially identical to said determinable surface pressure distribution; .and wherein said control means provides an additional adjustable flow rate of control fluid at said second depression for producing a resultant adjustable force at said second depression; whereby said adjustable forces are controllably applied to alter the position, orientation and motion of said craft in its fluid medium.

12. The system of claim 11 wherein said first and second depressions are in the shape of a right-angle step in the respective surfaces of said foil, and wherein said control means distributes the control fluid along the bases of said steps.

13. The system of claim 12 wherein said steps extend across the span of the foil and between predetermined chord points, and wherein said control means includes a plurality of orifices distributed along the width of each of said steps for admitting said control fluid to said step.

14. The combination according to claim 10 wherein said foil has an aspect ratio of at least three.

15. The combination according to claim 10 wherein said depression is terminated inwardly of the ends of said foil.

16. The system of claim 11 further comprising end plate means disposed substantially in perpendicular rela tion to said surfaces and secured to opposite ends of the foil for preventing the leakage of control fluid flow from the foil surface to which said flow is supplied to the other foil surface.

17. The system of claim 16 wherein said control means further comprises vent manifolds associated with each of said steps, said vent manifolds being located beneath the surfaces of said foil, and means for conducting said control fluid between the vent manifolds and the orifices of said respective steps.

18. The system of claim 16 wherein said fluid stream 13 is a water stream and said control fluid is .air at atmospheric pressure.

19. The system of claim 16 further comprising a plurality of additional identical foil structures rigidly supported along the sides of said craft; and wherein said control means comprises means responsive to the roll of the craft to provide an amount of control fluid flow to appropriate respective depressions in said foil structures for producing a force to minimize the amplitude of the roll.

20. The system of claim 10, wherein said foil structure comprises a hollow cylinder having an inner and outer surface, said outer surface corresponding to said at least one surface; wherein each of said inner and outer surfaces have depressions therein at predetermined regions thereof; wherein said control means provides a plurality of additional adjustable flow rates of control fluid to said depressions, and wherein said fluid stream producing means produces a fluid stream around the out- Side surface of said cylinder, a second stream producing means producing a second fluid stream of higher velocity through the inner portion of the cylinder, thereby creating different predetermined surface pressure distributions along the inner and outer surfaces of the cylinder.

21. The system of claim 20 further comprising at least one additional identical cylindrical foil structure rigidly secured to said craft, and wherein said control means comprises means selectively applying control fluid to appropriate depressions in said foil structures for in turn selectively applying horizontal, vertical and rotational force to said craft.

22. The combination according to claim 20 wherein said second stream producing means is an impeller and a spider secured interiorly of said hollow cylinder and having a central hub for supporting a shaft of said impeller.

23. The combination according to claim 22 wherein the interior of said hollow cylinder is contoured to provide a constant volume region downstream of said impeller.

24. The pure fluid force generator according to claim 2 wherein said control means comprises means for differen- 14 tially applying control fluid flow to said first and second depressions.

25. The system according to claim 11 wherein said control means includes means for differentially applying control fluid flow to said first and second depressions.

26. The pure fluid force generator according to claim 10 wherein said foil structure is a closed three dimensional body of circular cross section at any point along its longitudinal axis, and wherein said depression is in the shape of a step which extends about at least a portion of the circumference of the body and between predetermined chord points.

27. A pure fluid force generator comprising:

a streamlined foil structure with at least one surface having a depression defined therein between predetermined chord points of the foil structure, said depression being in the shape of a step having a leading edge extending substantially perpendicular to the chord line of the foil and a base extending rearwardly along the foil from said leading edge;

control means responsive to application of pressurized fluid thereto for flowing a fluid stream at a selectively adjustable flow rate along a base of said step from the juncture of the leading edge and the base of said step.

References Cited UNITED STATES PATENTS 2,805,032 9/1957 Davis 114--66.5 3,006,307 10/1961 Johnson 11466.5 2,608,171 8/1952 Pearce. 2,669,961 2/ 1954 Thomas. 3,128,063 4/1964 Kaplan 244-42.4l

FOREIGN PATENTS 955,762 7/ 1949 France.

ANDREW H. FARRELL, Primary Examiner US. Cl. X.R. 244-42 

